The present invention relates to atomic absorption spectroscopy equipment generally, and more particularly to an electrodeless discharge light source system which is useable and adaptable with an atomic absorption unit designed for a hollow cathode discharge light source.
Atomic absorption spectroscopy is a valuable analytic tool which is used in qualitative and quantitative analysis of chemical constituents in a variety of applications. The uses range from medical technology to pollution control technology. An atomic absorption unit is basically a spectrograph coupled to the sample vapor cell, with a high intensity light source directing light through the sample cell, so that the sample absorbs the light of the characteristic wavelength. The intensity and uniformity of light from the light source are particularly important in defining the accuracy of the system. The most widely utilized light source for such an atomic absorption unit is a hollow cathode discharge light source, such as described in U.S. Pat. No. 3,264,511. The hollow cathode discharge device permits highly directional light emission with good stability. The emitted radiation is contained within a few narrow, well defined wavelengths characteristic of the material used in the cathode. The hollow cathode design has been found utilizable with a broad spectrum of elements, and has successfully permitted extension of the analytic technique to a broad range of industrial applications.
It is the general practice for such atomic absorption units to operate in a pulsed mode with the light source being switched on and off in synchronism with the internal functioning of the spectrograph. A normally used hollow cathode discharge device is switched on and off by electronic gating of the device current. The hollow cathode discharge device must also be accurately aligned with the spectrograph.
A recently developed light source for use in such atomic absorption units is an electrodeless discharge lamp. The electrodeless discharge lamp is merely a light transmissive envelope containing a radiation emissive vapor which is excited by radio frequency energy. Such electrodeless discharge lamps have been found advantageous for certain types of elements. A standard atomic absorption unit already in the field should therefore be desirably adaptable to permit usage with the newly developed electrodeless discharge light sources, as well as with the conventionally used hollow cathode discharge devices. Such adaptability must preserve the precise optical coupling of the light source with the spectrograph, and permit ready changeability, since the end user will desire to use one or the other type of light source depending on the element being analyzed. The standard power supply for an atomic absorption unit for use with hollow cathode discharge device where pulsed operation is typically a relatively high voltage short duration pulse typically about 600 volts. The electrodeless discharge devices are typically operated at frequencies ranging to several hundred megahertz with pulse repetition rates of 30 to 1000 hertz.